The present invention relates generally to films, both monolayer films and multilayer films, and particularly to packaging films. The present invention also relates to packages, especially packages having one or more seals, as well as packaged products. The present invention is particularly related to films suitable for sealing, especially heat sealing.
Multilayer films having one or more tie layers containing a blend of an ethylene/alpha-olefin copolymer and a plastomer and/or an elastomer, are known. Such tie layers are internal film layers which those of skill in the art recognize as being compatible with other compositions, i.e., suitable for direct adhesion to, for example, ionomers and polyethylene homopolymers and copolymers.
Multilayer films with one or more surface layers containing a blend of an ethylene/alpha-olefin copolymer and a plastomer, and/or an elastomer, are also known. However, such films have been used in a manner in which the outer blend-containing sealing layer is sealed to itself, and the package is a high strength, heat-resistant structure which has been used as dunnage bags (which contain air, and are used to stabilize loads during shipping, these films comprising an ethylene/alpha-olefin copolymer having a density of about 0.916 or greater) and for use in the packaging of water softener, i.e., salt pellets.
Ionomers such as metal-neutralized copolymers of an olefin and a carboxylic acid are also known for use in an outer film layer. Ionomers are advantageous in the (outer) sealing layer of a film because they melt at relatively low temperature and produce a relatively strong heat seal. However, ionomers are expensive relative to other polymers typically used in packaging films.
Since ionomer-containing resins are expensive, it would be desirable to use less ionomer, or no ionomer, without sacrificing the advantageous properties provided by ionomers, such as low seal initiation temperature, relatively high seal strength, relatively high hot tack strength, suitability for seals used in cook-in conditions, acceptable for food contact, etc. Furthermore, it would also be desirable to provide a film having a relatively thick layer or layers which undergo melt flow during sealing, so that the resulting seal is capable of sealing through or around surface imperfections, or contamination such as dust, fat, water, the product being packaged, e.g. food, such as meat. Of course, it would also be desirable to provide at low cost this relatively thick region capable of melt flow during sealing, i.e., using compositions which are inexpensive, especially compositions less expensive than ionomer.
The present invention is the result of a discovery that a polymer composition which includes two or more different polymers, in an outer sealant layer and/or a seal-assist layer in packaging films, provide the films with highly desirable sealing characteristics, including one or more of the following: (a) low seal initiation temperature, (b) high seal strength, (c) high hot tack strength, (d) suitability for seals used under cook-in conditions, and (e) acceptable outer layer for use in direct contact with food. Moreover, it is most significant that these compositions rival the sealing performance of ionomer compositions which currently set the standard of commercial performance with respect to sealing, while being substantially less expensive than ionomer compositions. Thus, the present invention permits the use of less ionomer, or no ionomer, without sacrificing the advantageous seal properties provided by ionomers.
Furthermore, the composition of the present invention can be used to provide a film having a relatively thick layer or layers which undergo melt flow during sealing, so that the film is capable of sealing through contamination such as dust, fat, water, the product being packaged, especially food, such as meat, as well as sealing around surface imperfections. Providing such a relatively thick surface of ionomer is often so expensive that it is not commercially cost-prohibitive. Thus, the present invention enables the use of relatively thick sealing layers, with their respective advantages as set forth above, in commercial applications which previously have been cost-prohibitive.
As a first aspect, the present invention pertains to a package comprising a seal of a first outer film layer to a second outer film layer. The first outer film layer comprises a composition. The composition comprises a first component and a second component. The first component comprises at least one member selected from the group consisting of polyethylene homopolymer, and ethylene/alpha-olefin copolymer. The second component comprises at least one member selected from the group consisting of elastomer, plastomer, and carboxyl-modified polyethylene. The second outer film layer comprises at least one member selected from the group consisting of ionomer, ethylene/acid copolymer, and carboxyl-modified polyethylene.
Preferably, the first outer film layer comprises from about 1 to 99 percent of the total thickness of the film in which it is present; more preferably, from about 3 to 75 percent; still more preferably, from about 5 to 40 percent; and yet still more preferably, from about 7 to 25 percent.
Preferably, the first outer film layer has a seal initiation temperature of from about 175xc2x0 F. to 300xc2x0 F.; more preferably, from about 175xc2x0 F. to 250xc2x0 F.; and, still more preferably, from about 175xc2x0 F. to 225xc2x0 F.
Preferably, the composition comprising the first component and the second component comprises from about 5 to 95 weight percent of the first component with from about 95 to 5 weight percent of the second component; more preferably, from about 50 to 90 weight percent of the first component with from about 10 to 50 weight percent of the second component; still more preferably, from about 80 to 30 weight percent of the first component with from about 20 to 70 weight percent of the second component; and yet still more preferably, from about 70 to 50 weight percent of the first component with from about 30 to 50 weight percent of. the second component.
As a second aspect, the present invention pertains to a package comprising a seal of a first outer film layer to a second outer film layer. The first outer film layer comprises a composition. The composition comprises a first component and a second component. The first component comprises at least one member selected from the group consisting of ethylene/vinyl acetate copolymer, and ethylene/acrylate copolymer. The second component comprises at least one member selected from the group consisting of elastomer, plastomer, and carboxyl-modified polyethylene. The second outer film layer comprises at least one member selected from the group consisting of ionomer, ethylene/acid copolymer, ethylene/vinyl acetate copolymer, and ethylene/acrylate copolymer.
Preferably, the ethylene/vinyl acetate copolymer has a vinyl acetate (polymerization unit) content of from about 1 to 26 weight percent; more preferably, from about 4.5 to 19 weight percent; an still more preferably, from about 6 to 19 weight percent.
Preferably, the ethylene/vinyl acetate copolymer has a density of from about 0.91 to 0.95 g/cc; more preferably, from about 0.92 to 0.95; still more preferably, from about 0.93 to 0.95. Preferably, the ethylene/acrylate copolymer has a density of from about 0.91 to 0.95 g/cc; more preferably, from about 0.92 to 0.95; still more preferably, from about 0.93 to 0.95.
As a third aspect, the present invention pertains to a package comprising a seal of a region of a first outer film layer to a region of a second outer film layer. Each of the outer film layers comprises a composition. The composition comprises a first component and a second component. The first component comprises at least one member selected from the group consisting of polyethylene homopolymer, ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, and ethylene/acrylate copolymer. The second component comprises at least one member selected from the group consisting of elastomer, plastomer, ionomer, and carboxyl-modified polyethylene.
As a fourth aspect, the present invention pertains to a multilayer film. The multilayer film comprises an outer sealant layer and a core seal-assist layer. The outer sealant layer comprises at least one member selected from the group consisting of ionomer, carboxyl-modified polyethylene, and ethylene/acid copolymer. The outer sealant layer has a thickness of from about 1 percent to 20 percent, based on a total thickness of the multilayer film; preferably 5 to 15 percent; more preferably 7 to 10 percent; still more preferably 6 to 8 percent. Preferably, the seal-assist layer has a thickness of from about 10 to 95 percent, based on the total thickness of the film; more preferably, from about 10 to 50 percent; still more preferably, from about 10 to 30 percent. Preferably, the total thickness of the outer seal layer together with the seal-assist layer is from about 0.15 to 3 mils; more preferably, from about 0.5 to 2 mils; still more preferably, from about 0.5 to 1 mil.
The core seal-assist layer comprises a composition. The composition comprises a first component and a second component. The first component comprises at least one member selected from the group consisting of polyethylene homopolymer, ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, and ethylene/acrylate copolymer. The second component comprises at least one member selected from the group consisting of elastomer, plastomer, ionomer, and carboxyl-modified polyethylene.
As a fifth aspect, the present invention pertains to a package comprising a seal of a first region of a first outer film layer to a second region of a second outer film layer. The first outer film layer comprises a homogeneous ethylene/alpha-olefin copolymer, and the second outer film layer comprises at least one member selected from the group consisting of ionomer, ethylene/acid copolymer, carboxyl-modified polyethylene. The seal has a strength of at least 2 lb/in; preferably a strength of from about 2 to 10 lb/in.; more preferably from about 3 to 10 lb/in.; still more preferably, from about 5 to 10 lb/in.
As a sixth aspect, the present invention pertains to a film comprising a composition. The composition comprises a first component and a second component. The first component comprises at least one member selected from the group consisting of polyethylene homopolymer, ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, and ethylene/acrylate copolymer. The second component comprises at least one member selected from the group consisting of elastomer, plastomer, and carboxyl-modified polyethylene.
As a seventh aspect, the present invention pertains to a film comprising a first layer, a second layer, and a third layer. The first layer is an outer sealant layer, and the first layer comprises a first composition. The first composition comprises a first component and a second component. The first component comprises at least one member selected from the group consisting of polyethylene homopolymer, ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, and ethylene/acrylate copolymer. The second component comprises at least one member selected from the group consisting of elastomer, plastomer, and carboxyl-modified polyethylene. The second layer comprising a second composition. The second composition comprises a third component and a fourth. component. The third component comprises at least one member selected from the group consisting of polyethylene homopolymer, ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, and ethylene/acrylate copolymer. The fourth component comprises at least one member selected from the group consisting of elastomer, plastomer, ionomer, and carboxyl-modified polyethylene. The first composition is different from the second composition.
As an eighth aspect, the present invention pertains to a multilayer film comprising a first layer and a second layer. The first layer is a seal-assist layer, and the first layer comprises a first composition. The first composition comprises a first component and a second component. The first component comprises at least one member selected from the group consisting of polyethylene homopolymer, ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, and ethylene/acrylate copolymer. The second component comprises at least one member selected from the group consisting of elastomer, plastomer, and carboxyl-modified polyethylene. The second layer is an outer sealant layer, and the outer sealant layer comprising at least one member selected from the group consisting of ionomer, ethylene/acid copolymer, and carboxyl modified polyethylene.
As a ninth aspect, the present invention pertains to a multilayer film comprising a first layer, a second layer, a third layer, a fourth layer, a fifth layer, and a sixth layer. The first layer is an outer sealant layer as well as a food-contact layer, and the first layer comprises at least one member selected from the group consisting of ionomer, ethylene/acid copolymer, and carboxyl-modified polyethylene. The second layer is an outer layer as well as being a non-food-contact layer. The third layer is a seal-assist layer, and the third layer is between the first layer and the second layer. The third layer comprises a first composition. The first composition comprises a first component and a second component. The first component comprises at least one member selected from the group consisting of polyethylene homopolymer, ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, and ethylene/acrylate copolymer. The second component comprises at least one member selected from the group consisting of elastomer, plastomer, ionomer, and carboxyl-modif ied polyethylene. The fourth layer is a memory layer, and the fourth layer is between the second layer and the third layer. The fifth layer is a tie layer, and the fifth layer is between the third layer and the fourth layer. The sixth layer is a tie layer, and the sixth layer is between the second layer and the fourth layer.